The present invention relates to corrosion-resistant stainless steel canisters for propellant gas-containing aerosol formulations for use in propellant gas-operated inhalers.
In propellant-driven inhalers, the active substances are stored together with the propellant in cartridge-like canisters. These canisters generally consist of an aluminium container sealed with an aluminium valve cup in which a valve is embedded. A canister of this kind can then be placed in the inhaler in the manner of a cartridge and is either left there permanently or replaced with a new cartridge after use. Since chlorofluorocarbons (CFCs) were proscribed on the grounds of their ozone-destroying properties at the Rio de Janeiro Conference at the beginning of the 90s, the use of fluorohydrocarbons (FHC) is promoted as an alternative for use in propellant-driven inhalers. The most promising example to date are TG 134a (1,1,1,2-tetrafluoroethane) and TG 227 (1,1,1,2,3,3,3-heptafluoropropane). Accordingly, existing systems of delivery for treatments by inhalation have had to be converted to CFC-free propellants and new delivery systems and active substance formulations have had to be developed.
Surprisingly, it has been found that aluminium canisters are not always resistant to drug formulations containing fluorohydrocarbons as propellants but have a high risk of corrosion depending on the composition of the formulations. This is particularly true of formulations which contain electrolytes and/or free ions, particularly free halides. In these cases, the aluminium is attacked, which means that aluminium cannot be used as a casing material for the canisters. Similar instabilities in the aluminium canisters have been observed when fluorohydrocarbons are used as propellants if the formulations contain acid or basic components, e.g. in the form of the active substances, the additives, in the form of stabilisers, surfactants, flavour enhancers, antioxidants, etc.
One of the tasks of the present invention is to provide a canister for propellant-driven inhalers which is corrosion-resistant in the presence of active substance formulations for inhalation therapy containing a fluorohydrocarbon as propellant, which has sufficient compressive and breaking strength to withstand processing and use, which ensures the quality of the formulations stored therein and overcomes the other disadvantages known from the prior art.
The invention solves this problem by providing a canister for propellant-driven inhalers which consists predominantly of an alloy which is corrosion-resistant in the presence of drug formulations containing fluorohydrocarbons. The components of this alloy contain chromium (Cr), nickel (Ni), molybdenum (Mo), iron (Fe) and carbon (C). In another embodiment the alloy additionally contains copper (Cu), manganese (Mn) and silicon (Si). The canister according to the invention consists of a container (2) and a valve cup (8) with valve (9). The container preferably consists of one of the alloys described below. The invention therefore also relates to a container of this kind.
The invention further relates to the use of a container or canister of this kind consisting of a container (2) and a valve cup (8) with valve (9) in propellant-operated metering aerosols (inhalers) and a process for producing them.